The invention relates to high strength structural composites, and more particularly to a multi-layer fabric for reinforcing composites having increased flexibility in the longitudinal and lateral directions and sufficient thickness for use in forming planar and contoured composite structural parts, ballistics proof clothing, and the like. The fabric is particularly advantageous in making structural composites where curved or angular surfaces may be required by impregnating the flexible fabric which has been conformed to the desired shape and set with a resinous material. For example, curved body parts for automobiles, helicopters, boats, and the like, may be used by impregnating fabric flexed to conform to the shape of the part and set by resin. This provides not only a more light weight part, but one which is extremely strong and/or ballistic resistant.
Reinforced plastics are composites in which a resin is combined with a reinforcing agent to improve one or more properties of the plastic matrix. The resin may be either thermosetting or thermoplastic. Reinforced composites can be designed to provide parts ranging from toys to re-entry insulation shields and miniature printed circuits. The reinforcement is a strong inert material bound into the plastic to improve its strength, stiffness, or impact resistance. The reinforcing agent can be fibrous, powdered, spherical, crystalline, or whisker, and made of organic, inorganic, metallic, or ceramic material. Fibrous reinforcements may be natural, man-made such as synthetic and natural polymers, or carbon, textile glass, metal, ceramic yarns, etc. The fibrous reinforcement may be woven or non-woven. To be effective structurally, there must be a strong bond between the resin and the reinforcement. Conventional molding processes may be used to form the fiber reinforcing materials into a desired shape and impregnate them with a resin. To increase the strength, multiple single layers of fibers, fabrics, and the like, may be built up one at a time until the desired strength is reached. For example, the hand lay-up process for making fiber reinforced composite structures is one of the oldest and simplest methods. Male or female molds can be made from easily worked materials such as wood, plaster, or reinforced plastics. In hand lay-ups, resin and fibers in the form of fabric, woven roving, or mat are simply placed in the mold manually. Successive layers of fibers and resin can be added to build the part to the desired thickness. The problem with composite structures made from multiple layers of single layer woven fabric is that delamination can be a problem where only the adhesive matrix is holding the layers together. The composite layers are particularly vulnerable to shear forces. In the case of multiple non-woven fiber layers, proper orientation of the fibers in the successively formed layers is also a problem to which considerable attention need be given.
It is known to use multi-layer fabric wherein layers are mechanically secured together by woven yarns in numerous constructions. Examples of these fabrics are shown in U.S. Pat. Nos. 453,288 (carpet fabric); 1,335,311 and 4,580,611 (tire fabrics); Canadian No. 643,411, U.S. Pat. Nos. 2,816,578, and 2,899,987 (ballistic fabrics); and 3,749,138 and 4,174,739 (thick tubular fabrics). However, conventional multi-layer fabric has been typically woven with a warp element which undulates between the outer faces of the fabric. The weft yarn, however, is typically woven straight through the fabric. Because the weft is woven straight through the fabric, there are formed multiple layers of generally parallel lamina composed of the straight weft yarns in the lateral direction tending to impair lateral flexibility.
U.S. Pat. No. 2,495,808 and British Patent No. 2,066,308 disclose multi-layer fabrics which are impregnated with a gum and resin, respectively. The fabrics are woven with an undulating yarn between the outer faces woven in the longitudinal direction only.
French Patent No. 427,677 discloses a felt or velvet-like fabric which can have any desired thickness. To produce the felt-like velvet fabric, the warps are arranged in layers having progressively fewer yarns. Both the weft and warp yarns are indicated to follow the same slanted course, some of which go through the entire thickness of the fabric while the others only go through a portion of that thickness.
While prior art multi-layer fabrics have been woven in many multi-layered forms for different applications, the transfer of multi-layer fabric technology has not been readily made to the field of reinforced composite structures. In particular, the prior multi-layer fabrics have not been entirely suitable or satisfactory for the manufacture of contoured structures, particularly for reinforced composite structures or ballistic clothing where uniform flexibility is desired in all directions.
Accordingly, an object of the present invention is to provide a woven multi-layer fabric and process for manufacturing composite structures having uniform flexibility.
Another object of the invention is to provide polymeric structural composites having increased strength using multi-layer fabrics with uniform flexibility and thickness.
Another object of the invention is to provide a multi-layer fabric having uniform lateral and longitudinal flexibility so that the fabric may be made to conform to a variety of contours and shapes for the manufacture of reinforced structural composites.
Another object of the invention is to provide a multi-layer fabric having a weave which provides uniform directional flexibility and a mesh which may be effectively impregnated with a conformal material for setting the fabric in the form of a desired structural part.
Another object of the invention is to provide a multi-layer fabric having weave which provides increased flexibility, and a mesh and thickness which effectively protects against the intrusion of ballistic particles.
Another object of the invention is to provide a process for making and manufacturing contoured composite articles and parts by using multi-layered fabrics having uniform flexibility and sufficient thickness to be conformed to a shape of a desired structure and a mesh which can effectively be impregnated with a resin for setting in that shape.
Another object of the present invention is to provide a process for making and manufacturing contoured articles and parts by using multi-layered fabrics having uniform directional flexibility which are conformed to the shape of the article or part and then impregnated with the resin whereby the resulting article or part is light weight, yet has high structural integrity and/or is effective against ballistic projectiles.